1. The Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to methods employing etchants for etching oxides of silicon during the manufacture of a semiconductor device such that the selectivity of the etchant is low. The methods of the present invention are also useful in removing contamination other than silicon oxides typically encountered in semiconductor manufacturing process flows, such as polymer residues, while providing low selectivity.
2. The Relevant Technology
In the continuing quest for ever denser DRAM devices, the problem of forming for each memory cell capacitors having both sufficiently large capacitance to preserve a charge between refresh cycles and sufficiently small size to allow further reductions in circuit dimensions has become increasingly acute. Dimensional tolerances in capacitor formation have thus tended to become a yield-limiting and density-limiting factor in DRAM devices.
Clean processes are a significant source of decreased dimensional control in the formation of capacitor structures. Removal of native oxides and other types of oxide contamination is required at various steps during capacitor formation. A short dip in a dilute solution of hydrofluoric acid (HF), such as a 100:1 volumetric ratio of water to 49% HF solution, is typically employed for this purpose. Problems arise because the dilute HF solution also significantly and even preferentially attacks doped silicon dioxide such as BPSG in which the capacitor structures are formed and defined, resulting in decreased control of critical dimensions associated with the capacitor. A less selective process is thus needed to remove native oxides and other types of oxide contamination during capacitor formation without excessively attacking doped silicon dioxide such as BPSG.
A dilute HF solution is also typically employed to remove native oxide or other oxide contamination at process steps during which a refractory metal silicide such as titanium silicide is exposed to the solution. This may occur, for example, in a clean step prior to the formation of spacers around a gate stack that includes a refractory metal silicide layer, or during a clean step prior to filling a contact to a gate stack that includes a refractory metal silicide. As dimensions of gate stacks decrease, this use of dilute HF solution creates problems because the refractory metal silicide layer is preferentially etched by the dilute HF solution, such that where dimensional tolerances are small, the refractory metal silicide layer may be seriously damaged or even completely destroyed. A less selective process is thus needed to remove native oxide and other types of oxide contamination during gate formation and contact formation without excessively attacking refractory metal silicides.
An object of the present invention is to provide a method for removing native oxides and other types of oxide contamination during capacitor formation without excessively attacking doped silicon dioxide such as BPSG.
Another object of the present invention is to provide a method for removing native oxides and other types of oxide contamination without excessively attacking refractory metal silicides such as titanium silicide.
Still another object of the present invention is to provide a method for cleaning a surface having exposed doped silicon dioxide such as BPSG without removing significant amounts of the exposed doped silicon dioxide.
Still another object of the present invention is to provide a method for cleaning a surface having an exposed refractory metal silicide such as titanium silicide without removing significant amounts of the exposed refractory metal silicide.
In accordance with one general embodiment of the present invention, a surface having exposed doped silicon dioxide is cleaned with a buffered HF and ammonium hydroxide solution, resulting in removal of oxide contaminatiol or polymer residues wit decreased erosion of the doped silicon dioxide.
In accordance with another general embodiment of the present invention, a surface having an exposed refractory metal silicide is cleaned with a highly buffered HF solution, resulting in removal of oxide contamination with decreased erosion of the refractory metal silicide. This general embodiment is particularly useful in cleaning gate stacks prior to spacer formation and in cleaning contacts including contacts to gate stacks prior to contact fill.
In accordance with a method of the present invention, a capacitor contact formed through a layer of doped silicon dioxide to an active area of a semiconductor substrate is cleaned by either a highly buffered HF solution or by a buffered HF and ammonium hydroxide solution prior to the deposition of polysilicon to form the container of a container capacitor. The use of either of the above etchants to perform the capacitor contact clean decreases the amount of doped silicon dioxide removed by the capacitor contact clean, thereby reducing the likelihood of shorts between adjacent capacitors.
In accordance with another method of the present invention, a post-chemical mechanical polishing clean is performed to remove silica particles and other contamination remaining after isolation by chemical mechanical polishing (CMP) of polysilicon containers in doped silicon dioxide. Either a highly buffered HF solution or by a buffered HF and ammonium hydroxide solution is employed, resulting in less erosion of the doped silicon dioxide, providing better process control and less likelihood of subsequent formation of stringers.
In accordance with yet another method of the present invention, a contact to an active area of a semiconductor substrate formed through a layer of doped silicon dioxide containing container capacitors is cleaned, prior to filling the contact, with either a highly buffered HF solution or by a buffered HF and ammonium hydroxide solution. Use of the above cleaning solutions reduces the removal of doped silicon dioxide during the clean, decreasing the likelihood of a short from the contact to a container capacitor.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.